In the operation of steam and boiler systems, it is often the case that steam is available for use at a temperature much greater than is necessary or desired for a particular end use. In such cases, it is customary to utilize a so-called desuperheater, by which water is injected into a flowing stream of high temperature steam and mixed therewith. Ideally, the injected water itself almost immediately turns to steam, serving to convert the incoming, high temperature steam to a somewhat larger volume of steam at a somewhat lower temperature, i.e., with less superheat.
An earlier patent granted to Sanford S. Bowlus, U.S. Pat. No. 2,945,685, discloses an advantageous form of automatic desuperheater device, known as a variable orifice desuperheater. In the device of the Bowlus patent, incoming steam, traveling vertically upward through a desuperheater housing inlet, was arranged to lift against gravity a weighted valve element. The extent to which the valve element opened is automatically a function of the volume and velocity of the incoming steam. Surrounding the weighted valve element is a small orifice communicating with a source of desuperheating water. When steam is flowing through the system the weighted valve is lifted, resulting in a high velocity flow of the steam around the valve and an atomizing action of the steam on the surrounding water. The arrangement is such that, relatively independently of the volume of steam flow within reasonable limits, there will be an effective atomizing action of the steam upon the water. The amount of water injected into the desuperheater and combined with the incoming steam is controlled independently, as a function of steam temperature.
In basic principle, the variable orifice desuperheater of the Bowlus U.S. Pat. No. 2,945,685 is highly effective in operation. Thus, the present invention seeks to utilize the significant operative principles of the earlier Bowlus patent, while at the same time incorporating such principles into a substantially improved physical embodiment, which is more compact and rugged than prior devices and at the same time less costly to produce. These advantages are achieved without sacrifice of performance and, indeed, with improvement in performance in certain respects.
In accordance with one aspect of the invention, an improved variable orifice desuperheater is provided which includes a plug-type valve slideably guided within the desuperheater housing (a feature in itself previously known) which cooperates with a valve housing and valve seat structure in a unique and advantageous way to simplify and reduce the cost of construction of the unit. In accordance with this feature, the housing of the desuperheater unit is constructed with an internal, cylindrical valve guide, which is welded or otherwise secured in the interior of the housing. The housing is then welded closed, except that the opening at the inlet or lower end thereof is sufficiently large to receive the cylindrical valve plug and a sleeve-like member forming the valve seat. After the main housing has been welded closed, the valve and valve seat elements are slideably inserted through the bottom or inlet opening, with the valve seat being secured in position in the inlet passage.
As a more specific aspect of the invention, the inlet passage of the housing, and the sleeve-like valve seat element, are formed with mutually engaging shoulders, against which the sleeve-like element is seated for precise positioning of the valve seat relative to the water injection orifice area of the valve. This assures that, upon final assembly of the valve and valve seat elements, the working components of the desuperheater valve will be precisely positioned within the housing.
In accordance with another advantageous feature of the invention, the so-called mixing chamber, heretofore thought to be necessary to be provided within the desuperheater, is eliminated altogether, and the enlarged region of the desuperheater housing is reduced to a practical minimum of height. In this respect, the housing is necessarily enlarged in diameter, in relation to the diameter of the flow piping, in order to accommodate the flow of steam and injected water around the valve and valve guide area. Heretofore, it has been thought necessary to extend the enlarged diameter housing for a substantial distance beyond the valve area, before reconverging the flow back into the regular piping system. Pursuant to the present invention, however, the housing is brought back to normal diameter, and the flow of desuperheated steam is converged back to the diameter of the basic piping system almost immediately after the steam flow passes the upper end of the valve structure. This enables significant structural improvement in the overall unit, as well as a great savings in material and construction time. At the same time, the necessary mixing action is enabled to occur, partly within the minimum size housing and the balance within the piping system itself.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompanying drawings.